weed killer vs herbicide

weed killer and herbicide both are nouns.

Word	Noun	Adjective	Verb	Adverb
weed killer	Yes	No	No	No
herbicide	Yes	No	No	No

As nouns, weed killer and herbicide are synonyms defined as:

weed killer and herbicide: a chemical agent that destroys plants or inhibits their growth

Other synonyms of weed killer include weedkiller.

weed killer (noun)	herbicide (noun)
a chemical agent that destroys plants or inhibits their growth	a chemical agent that destroys plants or inhibits their growth